Protective devices are frequently used to protect electrical equipment from damage and guard against fire caused by overheating of the equipment. These devices are sometimes referred to as "thermal cut-off" since they are responsive to overheating and can interrupt the electric flow to guard against damage or fire.
Conventional thermal cut-off devices usually comprise a generally tubular heat-conductive body or casing having electrically conductive lead wires wherein each of said wires has an end protruding from the casing for connection to an electrical circuit, while their other ends are within the casing and are in contact with one another during the closed circuit conditions. The contacting ends may be held together by a fusible metal ring or solder, or a fusible plastic mass may be disposed within the casing which, at closed circuit conditions, biases one end of one of the lead wires to contact the end of the other lead wire. When the device is electrically connected to the electrical equipment which is to be protected, it will become heated due to passage of electric current, and if the casing temperature exceeds the melting point of the plastic, or the fusion point of the metal ring or solder, the plastic mass, the metal ring or the solder, as may be the case, will melt or will at least soften sufficiently to disengage the contacting ends of the lead wires, and hence interrupt further flow of electricity by opening the circuit.
The prior devices, however, have not been satisfactory due to one or more deficiencies which will become apparent from the ensuing detailed description of the present invention.
Accordingly, it is an object of this invention to provide an improved thermally responsive electrical cut-off device.
It is also an object of this invention to provide such thermal cut-off device which can rapidly and effectively protect electrical equipment against damage or fire caused by overheating due to excessive flow of electrical current.
It is a further object of this invention to provide such a protective device which prevents re-establishment of the current flow once the circuit has been opened.
The foregoing objects and other features and advantages of this invention will be appreciated from the following detailed description and the drawings.